The healthy cartilage of joints (articular cartilage) in humans and other mammals is characterized by a columnar growth pattern of chondrocytes, which produce a hyaline cartilage predominantly containing proteoglycans, type II collagen, and water. Articular cartilage, which covers each end of the long bones in vivo, is a smooth white structure. The structure of the articular cartilage is significantly different from that of the cortical bone beneath it. Articular cartilage does not have any blood vessels or neurons, so its nutrients are absorbed from the surrounding joint fluids, and thus, nutrients are provided slowly, resulting in relatively slow metabolism. Bone tissues have abundant blood vessels and nerve networks, such that their metabolism is very fast. Also, because a nerve system exists in bones, any impact or rubbing of two bones can be serious and painful. Because the surfaces of articulating bones in mammalian joints are covered with articular cartilage, bones do not come in direct contact with each other, so a person will not suffer discomfort when walking or performing intense movement. Articular cartilage provides an effective weight-bearing cushion to prevent bone-to-bone contact of opposing bones in a joint and, thus, is critical to the normal function of the joint.
Articular cartilage defects may be caused by wear over time, mechanical injuries or diseases. Many arthritic diseases and different degrees of trauma can cause destruction or deterioration of this fragile layer, leading to pain, joint stiffness, and even crippling disability. For example, joints are worn down over time; mechanical injuries are caused by accidents, causing the cartilage to tear and break down; and cartilage is eroded because of diseases, such as gout, rheumatoid arthritis and osteoarthritis. It is generally believed that, because articular cartilage lacks a vasculature, damaged cartilage tissue does not receive sufficient or proper stimuli to elicit a repair response. Once the articular cartilage becomes damaged, it cannot repair itself and therefore is worn down gradually. In addition, if the bone underneath the articular cartilage becomes damaged, pain or swelling may occur, resulting in difficulty walking and affecting daily life.
Since joint cartilage in adults does not naturally regenerate once it is destroyed, damaged adult articular cartilage has historically been treated with a variety of surgical interventions including repair, replacement, or excision. Articular cartilage defects have traditionally been treated with chondroplasty, shaving, microfracture, abrasion arthroplasty and, most recently, autologous transplantation. Early on, the treatment of articular cartilage defects was principally concerned with preventing a progression of the defect. More recently, attention has been focused on developing ways to actually repair the defect and effect articular cartilage healing. U.S. 2005/0125077 provides biocompatible tissue implants for repairing tissue injury or defects, wherein the tissue implants form a biological tissue slice that serve as a source of viable cells capable of tissue regeneration and/or repair, and can be harvested from healthy tissue to have a geometry that is suitable for implantation at the site of the injury or defect. However, this prior art reference did not teach nor suggest the optimal method for repair of articular cartilage defects. Moreover, the xenograft and xenogenous biomaterials may cause immunological problems, and the aforementioned is not the method most suitable for solving problems with the repair and treatment of articular cartilage defects.
Treatment of articular cartilage defects may be either surgical or non-surgical. Several operative procedures are currently used to repair or remove damaged cartilage in order to prevent further destruction of the joint, decrease pain, and restore function. These include arthroscopic debridement and lavage, subchondral bone stimulating procedures, transplantation of chondrocytes or cartilage autografts and allografts, and total knee arthroplasty. The traditional surgical process for treating articular cartilage defects or degeneration involves two procedures. In the first surgical procedure, a small biopsy of articular cartilage is performed, which is then transported to a laboratory specializing in cell culture for amplification. The tissue biopsy is treated with enzymes that release the chondrocyte cells from the matrix, and the isolated cells will be grown for a period of 3 to 4 weeks using standard tissue culture techniques. Once the cell population has reached a target number, the cells are sent back to the surgeon for implantation during a second surgical procedure. This manual labor-intense process is extremely costly and time consuming. Although clinical data suggests long term benefits for the patient, the prohibitive cost of the procedure combined with the traumatic impact of two surgical procedures to the knee have hampered adoption of this technique. Because the patient will have to endure the trauma of two surgical operations, the cartilage defects typically take a long time to repair. Furthermore, cell culture in vitro has many disadvantages, such as contamination.
Therefore, there remains a need for an effective method of repairing articular cartilage defects and injuries, one which can provide a time-saving surgical procedure, a faster recovery process, and beneficial reparative effects.